1. Field of the Invention
This invention relates to an inferential coriolis mass flowmeter, and more particularly to an inferential coriolis mass flowmeter for determining a mass flowrate of a fluid by using algorithm derived partially from Coriolis Force.
2. Description of Related Arts
A Coriolis mass flow rate measuring unit is a well-known device to measure flow rate of a liquid based on its mass. Coriolis Effect is used to measure the mass flow rate of a liquid. Coriolis Mass Flowmeter (CMF) is often used because CMF can measure flowrate more accurately without being affected by fluid density changes. Then the mass flow rate is converted to another well know unit such as volume flow rate. In industries especially oil and gas industry, Coriolis mass flow rate has been the most extensively used to measure flowrate within Coriolis Mass Flowmeter dispenser worldwide. Conventional CMF is manufactured bulky in size and the cost is usually higher due to its complex manufacturing process. External noise such as vibration is the major weakness in the conventional CMF. The accuracy of the conventional CMF is reduced when such noises are presence nearby.
GB Patent No. 2428090 (A) disclosed a flow meter that has a vibratable flowtube, a sensor connected to the flowtube for sensing motion of the flowtube and a driver connected to the flowtube to drive the flowtube. Random frequency signals are generated by a random frequency signal generator, and the signals are sent to the driver during a first mode of operation of the flowmeter. A second mode of operation may be carried out using a second drive signal. The flowmeter can measure mass flow rate or density of the fluid. A temperature or pressure sensor may be provided. The cited patent includes additional parts such as sensors and random frequency signal generator to enhance the accuracy of measuring the mass flow rate of a liquid. Additional partrenders complex design and complex manufacturing process which resulting higher cost.
U.S. Pat. No. 6,868,740 B2 disclosed a Coriolis mass flow meter that uses a measuring line attached with a tension sensor to record the mechanical tension of the measuring line. The tension sensor is connected to a pressure signal output facility to transmit a tension signal. A pressure signal is determined based on the tension signal generated by the pressure signal output facility. The cited patent is basically using a tension sensor to detect pressure difference of the measuring line. The result obtained is directly from the output signal of the tension sensor which may not be accurate especially when there are external factors such as temperature and liquid composition may involve.
U.S. Pat. No. 5,594,180 disclosed a device and method for detecting and correcting various fault conditions in an operating Coriolis mass flow meter. In this patent, information from a Coriolis mass flow meter is received and compared to threshold signatures representing various fault conditions. When a fault condition is detected, output signals inform an operator and control the mass flow rate to correct the fault condition. Particularly, the invention of the cited patent relates to detecting cracks in flow tubes to stop the flow of material through cracked flow tubes. The cited invention also detects the void fraction of material flowing through the tubes, determines a corrected actual mass flow rate and controls the mass flow rate to compensate for the void fraction. However, the cited patent is still using conventional Coriolis Effect in which the result can be affected by external noises such as vibration.
US Patent Publication No. 2007/0017304 A1 disclosed a Coriolis mass flow meter. This patent has at least one oscillator and sensor mounted on a Coriolis measuring tube for detecting Coriolis forces and oscillations from Coriolis forces. The cited patent provides means to detect zero flow in the measuring tube regardless of detection of Coriolis forces and oscillations from Coriolis forces. The means can be a sensor for measuring a flow according to a magnetic-inductive measuring method, the method for measuring the difference in propagation time or the Doppler method with aid of noise signals, a differential pressure method, a calorimetric method and a float-type measuring method. This patent is developed from a conventional CMF which uses mass flow rate basis.
Accordingly, it can be seen in the prior arts that there exists a need to provide a flowmeter which can easily manufacture and smaller in size without jeopardizing the measurement accuracy.